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Volume Number: 22 (2006)
Issue Number: 7
Column Tag: Reviews

Kool Tools

Solar Star Attic Fans

By MacTech Review Staff

Saving Energy on Cooling

Here in Southern California (where MacTech's main offices are), Edison has just had their 3rd rate increase of the year, and we're at about 40 cents per kilowatt hour. Most MacTech readers like knowing about gadgets for the home, so we thought we'd bring you a bit of information on a more practical product.

If you have an attic, you probably know that attics get hot, up to 120-150 degrees in the height of summer. A hot attic conducts heat into the rest of your home or office, or at the very least prevents it from going out. Even during the winter, proper ventilation helps prevent condensation from forming inside the attic. That can cause a variety of problems including significant heat loss from the home if the attic insulation gets wet.

In looking at the solutions, we took a look at Solatube's Solar Star attic fans specifically because they were solar powered, and therefore would be an easier install, and a more transparent pay back.

Solatube's Solar Star Attic Fan



What's different about this product other than solar power? The Solar Star has no thermostat or switches, and runs whenever sunlight strikes the solar panel. There are therefore, no electrical hookups, no operational costs, and a quicker installation process. Also, the 5-year warranty Solar Star Solar panel is high-impact resistant, providing protection from hail, wind, and damage from foreign objects.

Solar Star offers two versions, the gable vent attic fan and the roof mount attic fan. We took a look at both. They are very similar in the way they work, and what they do, but clearly, the roof mounted unit works better simply because the laws of physics (heat rising) work with it. The flip side is that the gable fan is an even easier install.

The fan units come fully assembled, are leak proof, and provide up to 1,200 square feet of circulation coverage. The gable fan comes with 15 feet of cable for you to use between the fan and the solar panel.

The fans can move up to 850 cubic feet per minute (depending on sunlight conditions). Obviously, these systems run best when the solar panel is under direct sunlight (e.g., south facing roof). Since there are no batteries on the fans, they do not run at night. When there is shade and provided the sky is bright, the fans run, but at a slower speed. When there is shading for a longer portion of the day, an add-on solar panel can be installed for better performance.

Installation

Installation really depends on your type of roof. If you have a composite roof, it's no big deal. But, if you have a tile or concrete roof, you should really get an experienced roofer to do the job. In our case, we went with one of Solatube's recommended installers, Competitive Roofing of Camarillo.



In the case of a composite roof install, it's about as easy as cutting the hole and fitting the unit in. Make sure that you have the right type of flashing to install your unit (see the Solatube web site for more on this), and in the more difficult installations, your roofer may want to fashion something that matches your roof.

Results

What good would a MacTech article be without some hard core testing and results. A solar powered attic fan is a neat concept, but does it work? In short ... absolutely. Astoundingly well in fact.

First, many attic fans are loud - you can many times here them inside the house. The Solar Star products are very quiet, and you cannot hear them inside. Even in the attic, they are quieter than the central air unit's fan.

Second, since the fan starts the moment the sun comes up, the attic stays ventilated all day, not just when it's hot enough to kick the thermostat on.

It's all about the temperature differences, right? Well, yes and no. On average in our monitoring, the attic was 7 degrees cooler at a variety of times of the day. If you are thinking in terms of averages, 7-10 degrees is a pretty good number. On the hottest of days, we saw a difference of as much as 12 degrees in the attic. Pretty impressive when you consider how quiet this 850 cfm fan is.

But what was really impressive is how much faster the attic cooled down at night. Prior to the attic fan, it could be 110 degrees in the attic long after midnight. With the Solar Star installed, we saw temperature drops of 1 degree every 10 minutes. As a result, after dinner, we would typically see comfortable attic temperatures.

Why is this important? If you are in a typical two story house, as our example was, the upstairs have bedrooms. Really the only time you care about the bedrooms being cool is at night. The cooling upstairs is working against the hot attic ... the cooler the attic, the easier it is to cool the upstairs. Same goes for a single story house.

The Gable Fan

For the gable fan testing, we went with a completely different use - venting the garage to keep it cooler. Garages tend to get warm not only from outside sources, but from cars with hot engines, water heaters, and more. In our test case, the Solar Star gable fan was able to cool the garage by approximately 10 degrees during the day.

Conclusion

Who cares what your attic temperature is? You only care what your cooling costs are, and how long it takes to cool your living areas. While there were too many variables to give you a definitive savings on electricity, it's clear that the AC had a much easier time cooling after the Solar Star was installed. Bottom line: The Solar Star made it considerably easy to cool the living area, and will easily pay for itself in electricity savings.

Retail prices for Solar Star Attic Fans begin at $399, plus professional installation if required ($125 for simpler installs, more for more difficult installs). See http://www.solatube.com/res_solarstar.php for more information.

KILL A WATT

By MacTech Review Staff

Kill A Watt is a device that measures electricity usage of appliances. Armed with information, you can effectively reduce your power consumption. It is equipped with a large LCD that displays electricity consumption by the Kilowatt-hour, and helps users in tracking their electrical usage by the hour, day, week, month, and even an entire year.

This device can also be used to assess quality of power by monitoring voltage, line frequency, and power factor. Kill A Watt displays power consumption in volts, amps, watts, Hz, and VA also.



Using this device, results can be calculated with 0.2% accuracy. The operating and maximum voltages of Kill A Watt are 115, and 125 VAC respectively. Kill A Watt has maximum current rating of 15 A and maximum power rating of 1875 VA, weighs 5 oz., and its dimensions are 5 1/8 x 1 5/8 x 2 3/8 inches.

What was most interesting to us in using the Kill A Watt is that we were able to determine which computers used the most electricity. For example, we tested an Xserve Dual G5 machine and realized is consuming over $50/mo. in electricity. And, you can see how computers have gotten more advanced -a Mac Mini G4/1.42 GHz costs less than $5/mo to run, while a G4 Cube/450 MHz is closer to $10/mo.

We used this device to determine air conditioning costs for portable air conditioners as well. Very useful, and well worth the cost of the unit.

KILL A WATT retails for $39.95, and is available from a number of online resellers. For more information, visit: http://www.p3international.com/.


MacTech Magazine Editorial Staff

 

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